Currently, a blue light-emitting diode, or LED, is used in combination with a fluorescent material to create an LED device to give off white light. White light generally ranges uniformly from 400 to 600 nanometers (nm) in wavelength, but light which appears as a combination of red, blue, and green will also appear as white. By using indium gallium nitride in the LED, it is possible to produce an intense blue light. The blue light passes through a material which contains phosphors which fluoresce in red and green. The combination of blue, red, and green produces an intense light which appears white. Essentially, most of the blue light at 470 nm strikes the phosphors in the fluorescent material, and that light would be up-shifted such that the secondary green and red lights complement the residual blue light which escapes past the phosphors. This provides a final combination of light which appears as white to the human eye.
Unfortunately, it has been determined that the conventional approach of using a fluorescent material layered onto the blue LED produces an LED with a bright, white core surrounded by an annular ring of yellow followed by an annular ring of blue, followed by a final annular ring of yellow. These annular rings do not always occur in a predictable manner from LED to LED, so some LED's provide relatively uniform white light while others have variations of the annular rings.
It has been difficult to determine the cause of these rings and thus, difficult to determine how to solve this problem. Customers view the deviations from white as a defect in the LED.
The above problem occurs both in LED lamps as well as surface-mounted LED lights.